Fuel pump louder when running
 

Hey all,

I'm really in need of some help here. I have a 1971 c-10 pickup with a 2003 5.3l silverado motor in it. I have been having issues with the fuel system so bad that I could barely limp the truck home at about 5 m.p.h. My fuel pump seems to be making an expect able amount of noise when the key is in the run position but the truck is off. (I commanded the fuel pump to run via HP tuners) but shortly after I actually start the truck, the pump gets louder and louder and the truck starts to run worse and worse. I have cleaned the fuel tank completely, replaced the fuel pump, checked for voltage drop, and I have tried running the truck out of a gas can. Any help on what could be wrong and what to check next would be greatly appreciated. The only thing I haven't done is checked the fuel pressure as I don't have the tools for that and no parts store around me rent them out. I hope to get the truck running well within the week as I need it for school.

Thanks,
Avery

Re: Fuel pump louder when running
 

Fuel pressure is pretty much the first thing you need to check.

Are you running multiple fuel filters (in and out, or a prefilter and a postfilter)? If so, what micron?

A fuel pump being loud usually means its straining. If its having a hard time drawing fuel due to a restriction or mounting issue, it'll get loud. Same goes for if you have a blockage in the line, the pump will strain to push its volume past the restriction.

Also doublecheck and reground the fuel pump wiring. Bad connections or thin supply wiring can force the pump to draw less voltage than it wants, which will make the pump run very weak.

Re: Fuel pump louder when running
 

I pressure tester my fuel system and got these results...

Fuel pressure was initially 58 psi and with the fuel pump running with the engine off, the fuel pressure slowly decreased. When I started the truck. Fuel pressure was around 50 psi and when I revved the motor it would spike to around 60 psi. As the motor ran longer the same symptoms occurred as with the engine off. The fuel pressure slowly decreased and when revved still spiked but no longer to 60 psi.

Any suggestions on what to do?

Re: Fuel pump louder when running
 

55-60psi is normal operating range, so you want to have that range at all times. Unless its a Flex Fuel truck, it shouldn't be seeing less than 50psi, or much more than 60-65 on the high end.

A pump will usually bleed down pressure after the vehicle shuts off, at least to a certain extent. That isn't something that would cause the symptoms you describe.

When the truck is running, does the fuel pressure keep going lower and lower?

Re: Fuel pump louder when running
 

To answer your question first, as the truck was running, the fuel pressure got lower and lower, the pump got louder and louder, and the truck ran worse and worse. I tried several things to fix this.

The first thing I did was pull off the 40 micron filter I have before the fuel pump and let the pump pull fuel straight from the gas can. This seemed to keep the fuel pressure steady, without the pressure decreasing as the truck ran longer. The truck still seemed to idle like crap so I pulled the MAF sensor off while keeping the fuel filter off and it ran much better.

Since I changed two variables I put the fuel filter back on and started the truck. Fuel pressure was lower than before and the pump was considerably louder so I hope I have found the issue.

Is this plausible? I have spent all day cleaning and drying my fuel tank so it isn't an option to drive it yet to see if it runs better. If the fuel filter is at fault what can I do to fix this. Driving without a filter clearly isn't an option so should I go with a higher micron filter?

Thanks for the help. It's very much appreciated.

Re: Fuel pump louder when running
 

I usually run a 100 micron pre filter, i wouldn't use a 40. This is what i have and I've never had a problem (I'm using the small one). Made in USA and very reasonably priced. http://www.robbmcperformance.com/products/filters.html

Re: Fuel pump louder when running
 

Thank you for the link. Are you running their 10 micron filter as well after the pump?

Re: Fuel pump louder when running
 

I actually run a filter AFTER the pump only. I'm fine with in-tank pumps having strainers or socks, but on externals, I've had nothing but issues with pre-filters.

Some folks buy ones that aren't efi rated, or buy really cheap ones who's screens and cheap bodies don't last very long. Its also important to make sure you're using lines at least -6, preferably -8 if your making power. All that stuff contributes to restrictions. Since these pumps prefer to pump on the head rather than draw (meaning push, not pull), having a restriction on the inlet site is sorta like sucking through a collapsed straw.

I run a 255 and just keep an extra. I've never clogged or burned one out, and my routine fuel filter checks have all come up clean, even after more than 15k mi on my swap.

Re: Fuel pump louder when running
 

What micron filter are you running? I just purchased the 100 micron filter that was recommended. Is that an adequate filter to run after the fuel pump?

Re: Fuel pump louder when running
 

No, I'm running a factory type filter after the pump. If you're going to run their 10 micron filter after the pump, just make sure you don't mix them up! Just looking at them from the outside, they're going to be identical. ;) I have cleaned mine once at the 25k mile mark, and although it was far from clogged up, there was a significant amount of debris in it. Granted, I'm not sucking the fuel through the factory fuel sender sock, mine is gravity fed from the bottom of the tank.

Re: Fuel pump louder when running
 

Hi all,

Just wanted to give everyone an update on the truck.

I received the filter in the mail a few days ago and there was an immediate difference in fuel pump performance. I could hold a constant 60 psi. The last few days I have put around 100 miles on it and have had to clean the filter twice.

This isn't much of a surprise to me as the gas tank I have was very dirty and even after cleaning I think there must be a little bit of gunk in there. I'm just going to keep driving it and keep cleaning it until no more gunk comes out.

I appreciate everyone's help and advice. It's looking like I'll be able to take my truck to the first day of school which I'm very excited for. I haven't been able to reliably drive it for about a year.

Again,

Thanks.

Re: Fuel pump louder when running
 

:metal: